Preparation of zirconium for cold working



PREPARATION OF ZIRCONIUM FOR COLD WORKING Kenneth H. Dale, Louisville,Ky., assignor to Olin Mathieson Chemical Corporation, East Alton, 11].,a corpora- No Drawing. Filed Apr. 13, 1956, Ser- No. 577,921

12 Claims. (Cl. 204-32) This invention relates generally to metaltreating and more particularly to zirconium and to methods for placing ametallic coating thereon and to a process for cold working zirconium.

Zirconium, because of its low neutron absorption, is particularlyadvantageous for making containers and other metallic parts to be usedin conjunction with atomic engines and for the transportation ofradioactive material. A layer of an adherent abrasive scale is formed onzirconium when it is exposed to the air and zirconium has a rapid Workhardening rate. Consequently, it is extremely diificult to cold work themetal and a special treatment is required before it can be elongatedwithout fracturing by cold rolling, deep drawing, extruding and similarcold Working processes. One method for removing the scale from zirconiumavailable heretofore involves removing the scale by abrasive polishing,such as wire brushing and grit blasting. Then to improve thecold workingproperties of the metal, the freshly brushed surface is deeply etched ina chemical solution and coated with a layer of nickel by anelectroplating process. The plated metal must next be hardened to bringabout diffusion and alloying of the nickel with the zirconium. Such aprocess is laborious, requires the use of specialized expensiveequipment and, in order to recover a zirconium surface, the alloy mustbe machined from the surface. Zirconium has the additional undesirablecharacteristic of readily reacting with hydrogen, nitrogen and oxygenwhen heated and as a result it has been necessary heretofore to annealthe zirconium in vacuo'.

It is, therefore, an object of this invention to provide an improvedmethod for cold working zirconium. Another object of this invention isto provide a process for preparing zirconium for cold working. A furtherobject of the invention is to provide a method for placing on zirconiuma protective coating of another metal. A still further object of thisinvention is to provide a method for annealing zirconium in air; i.e.,without evacuating the annealing furnace. Still another object of theinvention is to provide a solution and process for removing scale fromthe surface of zirconium. A still further object of the invention is toprovide a solution for coating zirconium with a ductile metal. Anotherobject of the inventio'n is to provide a process for lubricatingzirconium while cold working. Another object of the invention is toprovide a means for coating zirconium articles with an adherent andsmooth deposit of a ductile material adapted to be removed by chemicalmeans without etching the surface of the zirconium article.

The foregoing objects as well as others are achieved in accordance withthis invention, generally speaking, by providing a solution for removingthe scale from zirconium by chemical means and a means for coating thecleaned zirconium surfaces with a coating of a ductile metal. Inaccordance with this invention, the scale is removed from the zirconiumby immersing the zirconium article in an aqueous solution of nickelsulfate, fluoride ions and an oxidizing agent such as hydrogen peroxide.

nited States Patent C) 2,938,841 Patented May 31, 1960 lot:

The cleaning is improved by including a minor amount of a wetting agentin the solution. The cleaned zirconium surface is first coated bychemical reduction with a layer of tin or zinc by immersing it in anaqueous solution of a soluble zinc or tin salt and fluoride ions andleaving it therein until the zinc or tin is deposited in a smoothadherent film on the zirconium. It has been found that zirconium coatedwith either tin or zinc has improved cold working properties overuncoated zirconium and that in some instances the cold workingcharacteristics of zirconium may be further improved by coating the tinor zinc coating zirco'nium with another ductile metal. When additionalcoatings are desired, the tin or zinc coated zirconium is first coatedwith a very thin film of copper. Such a film of copper is commonly knownin the industry as a copper strike. The copper surface may then becoated with a ductile metal by electroplating it in a suitable bath forelectroplating copper with copper or for plating copper with any otherductile metal such as brass, iron, tin, lead and the like or by means ofa suitable chemical reduction process. A more adherent coating isobtained when a copper strike is used even if the final coating is to becopper. A preferred solution from which copper may be electrolyticallydeposited over the copper strike is an alkaline cyanide copper solution.This solution may be used also for placing the copper strike on thearticle.

The total thickness of the coating or coatings of metal on zirconiummust be within the range of from about 0.001 inch to about 0.002 inchfor satisfactory cold working. If the thickness is greater than this,the coating peels from the metal during the cold working operation andthe zirconium is not properly protected if the thickness is less than0.0008 inch.

It has been found that the scale appearing on the surface of metalliczirconium after exposure to the atmos-' phere may be removed rapidlywithout etching the metal by immersing the zirconium in an aqueoussolution of from about 300 grams to about 700 grams of nickel sulfate(NiSO -7H O) per liter and fluoride ions in a concentration equivalentto from about 15 milliliters to about 30 milliliters of 48% hydrofluoricacid per liter at a temperature of from about 200 F. to about 210 F.Fifteen to thirty milliliters of hydrofluoric acid contain from about7.75 grams to about 15.5 grams fluoride ions.

Zirconium may be coated with zinc by immersing it in an aqueous solutionof from about 800 grams to about 1600 grams per liter zinc sulfate (ZnSO-7H 0), about 15 milliliters to about 30 milliliters 48% hydrofluoricacid (0.516 gram fluoride ion per milliliter) and from about 15 gramsto' about 30 grams per liter aluminum sulfate (Al SO Zinc is depositedupon the zirconium by chemical reduction in such a solution. Anysuitable zinc salt may be substituted for zinc sulfate, such as, forexample, zinc chloride, but the amount of zinc ion utilized in thesolution should be substantially equivalent to the zinc ionconcentration of the solution specified above. The fluoride ion may besupplied to the solution used to remove the scale from the zirconium andto the zinc coating solution by dissolving therein sodium fluoride,ammonium fluoride, ammonium bifluoride, potassium fluoride or potassiumbifluoride or any other suitable fluoride salt provided the amountthereof is within the fluoride ion concentration obtained by the use ofthe above amounts of hydrofluoric acid. The plating solution willdeposit a suitable coating of zinc on a properly cleaned zirconiumsurface by chemical reduction in from one-half to'- one minute while thesolution is at room temperature, or inother words, within theneighborhood of about 20 C.-

A suitable coating of tin may be applied to the properly cleanedzirconium article by immersing it in an aqueous solution of a salt andfluoride ions. A preterred ing from immersion in such a solution hasbeen found particularly well suited for lubricating zirconium in coldworkingoperations so thezirconium may be provided with a coating of fromabout 0.001 inch to about 0.002 inch tin and cold worked without anyother coating of ductile metal. In some instances, it may be necessaryto immerse the article longer than 10 minutes in order to obtain acoating of about .002 inch. If the metal is to be annealed, however, itis advisable to place a coating of copper or brass as described in moredetail hereinafter over the tin. In'those instances where other metalsare to be placed over the tin, the tin coating may be from about 0.0005to about 0.001 inch in thickness. Furthermore, if the amount ofreduction in thickness of the metal during cold working is relativelygreat the added protection of the copper, brass, or the like over thetin is sometimes desirable.

An aqueous solution found particularly well suited for placing, a thinfilm of copper over a zinc or tin coating on zirconium contains about165 grams per liter copper cyanide, about 195 grams per liter sodiumcyanide, about l20'grams per liter sodium carbonate and about 10 gramsRochelle salt. The solution should be at atemperature of between about120 F. and about 140 F. and the article should be. electroplated forabout two minutes at a current density of about 24 amperes per squarefoot after which time the current should be turned ofi. Thecurrentshould then be turned on and the article plated for. about 5 minutes atabout 12 amperes per square foot, to complete the copper strike. Thefilm of copper obtained is about 0.00001 inch to about 0.00002 inch. Ifno other metal is to be placed on the copper, the thickness of thecopper may be increased until the total thickness of the base coating oftin or Zinc, the copper strike and the final copper plate is about 0.002inch by continuing the plating treatment.

As stated above, zirconium having a thin copper strike coating may beplated with a thicker coating of a ductile material such as, forexample, copper, brass, tin, iron or the like in order to furtherimprove the zirconium cold working characteristics. Any suitableelectroplating solution for plating over copper may be utilized for thispurpose; The coating of these metals should be from about 0.0005to about0.0010 inch or of suflicient thiCk-.

ness that the total thickness of the coating on the zirconiuni is withinthe range of about 0.001 to about 0.002 inch if the metal is to be coldworked such as by drawing or rolling.

3 A solution suitable for placing a brass coating on copper has thefollowing composition:

9 to 12 grams per liter zinc cyanide 19 to 25. grams per liter coppercyanide 12 to 16 grams per liter sodium carbonate 28 to 35 grams perliter sodium cyanite Temperature, 75 F.-100 F. v

Current density, 2.5-.-15 amperes per square foot Voltage, 1.5-2

A solution particularly well suited for immersion plating zirconiumhavinga film of tin or zinc and a film of copper thereon with iron hasabout the following composition:

Ferrous sulfate, FeSO -7H O 660 grams per liter. Hydrofluoric acid (48%)HF 230 milliliters per liter.

sulfate, Al (SO 5 grams per liter.

Manganese sulfate, MnSO grams per liter. Sodium alkyl aryl sulfonate .2gram per liter. Temperature 150 F.

Time 5 to 10 minutes.

then rinsed in water at about 20 C. and is immediately immersed in asolution containing from about 300 to about 700 grams per liter nickelsulfate, 15 to milliliters per liter 48 percent hydrofluoricacid, 0.1 to0.2 gram per liter sodium alkyl aryl sulfonate orother suitable wettingagent and about 0.5 to l milliliter per liter hydrogen peroxide at atemperatureof between about 200 F. and 210 F. until the scale on thesurface of the zirconium has been removed.

The cleaned zirconium article is coated with a layer of Zinc from about0.0005 to about 0.001 inch thick by immersing it in a zinc platingsolution having the composition specified hereinbefore at roomtemperature. The

- zinc plating solution is rinsed from the article with Water and a filmof copper from about 0.00001 to about 0.00002 inch thickness is placedover the zinc by electroplating as described above After-the copperstrike has been placed on the metal, the current islturned off thesecond time. The copper coated zirconium may then be coated with one'ofthe ductile metals until the total thickness of coatings on thezirconium is within the range of about 0.001 inch to about 0.002 inch.The zirconium is then coated with glycerine and' cylindrical blanks arecut therefrom and the blanks are drawn and shaped into a cup byconventional cold working methods with a punch and die. It has beenfound that the coating adheres to the zirconium and elongates with it asit is cold worked and acts as a barrier between the cold working toolsand the zirconium if its thickness is within the range specified aboveand the coating thus materially increases the life of the tools withoutscratching or otherwise marring the surface of the zirconium. p

As indicated hereinbefore zirconium cleaned and coated in accordancewith this invention maybe heated to annealing temperatures withoutevacuating the annealing furnaces. Also annealing the coatedmetal iscleaned and pickled in a suitable aqueous solution and is then coldworked by rolling, drawing orsimilar process. The metallic coatingof tinor zincor the coating of one of these metals with another ductile metalsuch as iron, tin, copper and the like may be removed from the zirconiumby immersi-ng the article'in a suitable solvent forthe coating which isnot a solvent for thezirconium. After the coating has been removed, abright zirconium finish is obtained without any etching or other marringof the surface. I Although the invention has been described in considerable detail in the foregoing, it is to be understood that such detail issolely for the purpose of clarifying the invention and that variationscan be made therein by those skilled in the art without departing fromthe spirit and scope of the invention except as'it is limited by theappended claims. Iclaim: I V H l. The process for preparing zirconiumfor cold working which comprises removing the oxide scale; in an aqueoussolution of about 300 to about 700 grams nickel sulfate per liter,fluoride ions in a concentration equivalent to from about '15 to about30 milliliters of 48 percent hydrofluoric acid per liter and hydro genperoxide, coating the thus cleaned zirconium with a metal selected fromthe group consisting of tin and zinc by immersing it in an aqueoussolution selected from the group consisting of solutions of tin ions atleast equivalent to about 54 grams per liter of stannous sulfate withfrom about 15 to about 30 milliliters of 48% hydrofiuoric acid per literand solutions of zinc ions containing from about 800 grams to about 1600grams per liter of zinc sulfate (ZnSO -7H O), about 15 to 30 millilitersof 48% hydrofluoric acid per liter and from about 15 to about 30 gramsper liter of aluminum sulfate, electrolytically depositing a film ofcopper on the resulting surface, aud thereafter depositing a coating ofa ductile metal over the copper film.

2. The process of claim 1 wherein the zirconium is plated with zincafter cleaning.

3. The process of claim 1 wherein the zirconium is plated with tin aftercleaning.

4. The proca s of claim 1 wherein the final coating is copper.

5. The process of claim brass.

6. The process of claim 1 wherein the final coating is iron.

7. The process for preparing zirconium for cold Working which comprisesremoving the oxide scale therefrom in an aqueous solution of from about300 to about 700 grams nickel sulfate (NiSO -7H O) per liter, and fromabout 15 to about 30 milliliters of 48% hydrofluoric acid per liter at atemperature of from about 200 F. to about 210 F, coating the zirconiumwith zinc by immersing it 1 wherein the final coating is in a solutionof from about 800 to about 1600 grams per liter zinc sulfate (ZnSO -7HO), about 15 to about 30 milliliters 48% hydrofluoric acid per liter,from about 15 to about 30 grams per liter aluminum sulfate (Al (SO in anaqueous solution, depositing a coating of copper over the zinc byelectroplating with a current density of at least about 15 amperes persquare foot in a solution containing about 165 grams per liter coppercyanide, about 195 grams per liter sodium cyanide, about 120 grams perliter sodium carbonate and about 10 grams per liter Rochelle salt at atemperature of from about 120 F. to 140 F., and thereafter depositing acoating of a duotile metal over the copper strike.

8. The process for removing the oxide scale from zirconium whichcomprises immersing the zirconium in an aqueous solution consistingessentially of from 30 percent to 70 percent nickel sulfate, 1 percentto 3 percent hydrofluoric acid and minor amounts of hydrogen peroxideand a compatible wetting agent.

9. A process for producing zirconium having an adherent, ductileelectrodeposit of a metal on the surface thereof which comprises firstdepositing on the clean zirconium a coating of tin by chemical reductionin a solution consisting essentially of tin ions at least equivalent toabout 54 grams per liter of stannous sulfate with from about to about 30milliliters of 48 percent hydrofluoric 6 acid per liter, and thereaftercoating the zirconium with a ductile metal.

10. A solution for coating zirconium with zinc by chemical reductionwhich consists essentially of from 800 grams to 1600 grams per literzinc sulfate (ZnSO -7H O) about 15 milliliters to about 30 milliliters48 percent bydrofiuoric acid per liter, from about 15 grams to about 30grams per liter aluminum sulfate (Al (SO 11. A method of coatingzirconium articles with an adherent and smooth deposit of a ductilemetal which comprises cleaning the zirconium article to removesubstantially all of the surface oxide film, coating the cleaned articleby immersing it in a solution selected from the group consisting ofsolutions of tin ions at least equivalent to about 54 grams per liter ofstannous sulfate with from about 15 to about 30 milliliters of 48%hydrofiuoric acid per liter and solutions of zinc ions containing fromabout 800 grams to about 1600 grams per liter of zinc sulfate (ZnSO -7HO), about 15 to about 30 milliliters of 48% hydrofluoric acid per liter,and from about 15 to about 30 grams per liter of aluminum sulfate, andthereafter electrolytically depositing a coating of a ductile metalthereon.

12. A process for improving the cold working properties of zirconiumwhich comprises coating the zirconium with a film of ductile metal fromabout 0.001 to about 0.002 inch thick, said film being composed of alayer of tin adjacent the zirconium, a copper strike adjacent the tin,and an electrodeposited layer adjacent the copper strike of a ductilemetal selected from the group consisting of copper, brass, tin, iron andlead.

References Cited in the file of this patent UNITED STATES PATENTS1,248,107 Hathaway Nov. 27, 1917 1,948,485 Anselm Feb. 27, 19342,370,973 Lang Mar. 6, 1945 2,496,845 Balden et a1. Feb. 7, 19502,564,549 Stargarter Aug. 14, 1951 2,580,773 Heiman Jan. 1, 19522,624,684 Heiman Jan. 6, 1953 2,646,396 Dean July 21, 1953 2,653,134Dilling et a1 Sept. 22, 1953 2,711,389 Beach et a1 June 21, 19552,734,837 Hands Feb. 14, 1956 2,776,255 Hammond et a1. Jan. 1, 19572,798,843 Slomin et al July 9, 1957 2,801,213 Beuckman et al. July 30,1957 2,825,682 Missel et a1 Mar. 4, 1958 2,835,630 Huddle et al May 20,1958 OTHER REFERENCES Principles of Electroplating and Electroforming,Blum et 21.1., 3rd edition (1949), McGraw-Hill Book Company, Inc., NewYork, pages 379-381.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent Neg 29S8,84l May LII 1960 Kenneth Hc Dale It is hereby certified that errorappears in the-printed specification of the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

Colman 2. line "coating" read coated column 4 Tine 7 for "container"read containing line 13 for "ofi'" read of same column 4 line 50 for"Also" read After Signed and sealed this 8th day of November 1960o(SEAL) Attest:

KARL AXLINE ROBERT C. WATSON Attesting Oflicer Commissioner of Patents

1. THE PROCESS FOR PREPARING ZIRCONIUM FOR COLD WORKING WHICH COMPRISESREMOVING THE OXIDE SCALE IN AN AQUEOUS SOLUTION OF ABOUT 300 TO ABOUT700 GRAMS NICKEL SULFATE PER LITER, FLUORIDE IONS IN A CONCENTRATIONEQUIVALENT TO FROM ABOUT 15 TO ABOUT 30 MILLILITERS OF 48 PERCENTHYDROFLUORIC ACID PER LITER AND HYDROGEN PEROXIDE, COATING THE THUSCLEANED ZIRCONIUM WITH A METAL SELECTED FROM THE GROUP CONSISTING OF TINAND ZINC BY IMMERSING IT IN AN AQUEOUS SOLUTION SELECTED FROM THE GROUPCONSISTING OF SOLUTIONS OF TIN IONS AT LEAST EQUIVALENT TO ABOUT 54GRAMS PER LITER OF STANNOUS SULFATE WITH FROM ABOUT 15 TO ABOUT 30MILLITERS OF 48% HYDROFLUORIC ACID PER LITER AND SOLUTIONS OF ZINC IONSCONTAINING FROM ABOUT 800 GRAMS TO ABOUT 1600 GRAMS PER LITER OF ZINCSULFATE (ZNSO4 7H2O), ABOUT 15 TO 30 MILLILITERS OF 48% HYDROFLUORICACID PER LITER AND FROM ABOUT 15 TO ABOUT 30 GRAMS PER LITER OF ALUMINUMSULFATE, ELECTROLYTICALLY DEPOSITISNG A FILM OF COPPER ON THE RESULTINGSURFACE, AND THEREAFTER DEPOSITING A COATING OF A DUCTILE METAL OVER THECOPPER FILM.